SUMMARY OF THE INVENTION
1. Technical Area of the Present Invention
In a magnetic disk drive, a slider (or head) is flown above a spinning storage disk. Attached to the slider is a read/write transducer which transforms electrical pulses to small magnetic fields which are stored on the disk. The order of the magnetic fields and their subsequent orientation, aligned along the circumference of the disk in north-south configuration, defines a bit code capable of detection as the slider flies over the disk. The sliders are held in place above the disk by a metal spring structure known in the industry as a suspension. This suspension attaches to a rigid arm manipulated by a linear or rotary motion actuator designed to locate the slider at any radial position above the disk. The spinning disk coupled with the actuator movement serves to gain access to multiple tracks across the disk surface, each capable of containing stored data for later retrieval.
Signal transmission from the slider transducer to the amplifier and signal processing circuitry of the disk file, necessitates the need for an electrical interconnect between the dynamic, "flying" slider, and the static circuitry of the data channels. A printed flexible circuit routed from the signal processing circuitry to the vicinity of the actuator arms, connects with conductive wire(s) to complete the final path down the suspension to the slider.
The interconnect routed down the suspension typically contains a minimum of two conductors serving the slider transducer comprised of a single inductive element to read and write. Transducer designs may also incorporate a separate magneto-resistive read element and an inductive write element requiring a minimum of 3 wires if the elements are tied together or a minimum of 4 wires if the elements are completely separate. The dynamic requirements of flying the slider close to the disk surface (&lt;0.1 micrometer) necessitates minimum mass, stiffness, and size for this interconnect.
2. Description of the Prior Art.
This invention pertains to the interconnecting device spanning the suspension, from the slider transducer to the printed flexible circuit mating with or containing the signal processing devices. As the industry transitions to smaller slider/transducer sizes to increase data storage density, limitations of the current interconnecting devices increases the potential for read/write errors and imposes ceilings on data storage density.
Prior art portrays heavy reliance upon the use of small insulated copper wires (44 AWG or smaller diameter) threaded into PTFE tubing (0.25 mm-0.38 mm. in diameter). Enclosing the insulated copper wires within the tubing provides protection from potentially damaging vibrational contact with the suspension member. The PTFE tube typically extends from the suspension tip along the side or central rails, top or bottom surface of the suspension, to the base plate region and beyond. To avoid reducing the dynamic performance and flight characteristics of the slider, only the fine wires are routed past the suspension out to the slider bond sites. Among references to the use of the tube and wire interconnect include U.S. Pat. Nos. 5,012,368, 4,853,811, 4,991,045.
Limitations of the art encompass various areas. Manual conductor routing (along the suspension) and service loop shape setting, can induce unfavorable static slider bias or bias variability. Lack of orientation, placement, and spacing definition of free form twisted conductors at bond sites increases bias variability and bond positioning labor. Usage of suspension appendages termed "wire-crimps", to anchor PTFE tubular wire sheaths, have the potential of inducing internal stresses to the suspension and damaging the twisted conductors. Profile limitations imposed by PTFE tubing and wire crimp tabs can limit disk stack height. Individual positioning and bonding of conductors to the slider and amplifier/signal processing electronic cable can require significant labor. As the head suspension assembly becomes more automated, the manual routing/bonding of the tube and wire interconnect poses an obvious constraint.
Other interconnect inventions detail the usage of flat or round conductive wires laminated within plastic film layers (i.e. flexible printed circuitry: additive or subtractive), playing upon the advantages of low profile, controlled impedance, spaced leads, and favorable dynamic response. These basic U.S. patents include #'s 4,819,094, 4,670,804, 4,645,280, 4,616,279. As referenced in U.S. Pat. No. 4,645,280, the flexible printed circuit interconnects are often adhesively bonded to the suspension structures. Although profile, electrical performance, and automation compatible advantages of printed flexible circuitry as interconnect prove favorable, the economic impact of high volume usage must be considered. In addition, film substrates used within flexible printed circuitry can lend a higher stiffness value to the interconnect in the vicinity of the service loop area. Materials thin enough to negate this factor are difficult to work with.
A third representation of prior art involves the utilization of plastic compounds either complementing the function of (such as a thin film overlay) or comprising an integral element of the suspension structure. The conductive wires of the interconnect can either be heat staked or molded into plastic structure providing advantages of low profile, favorable dynamic response, and protective attachment to the suspension. U.S. Pat. No. 4,991,045 details such a composite suspension design, while U.S. Pat. Nos. 5,006,946 and 5,001,583 detail conductors contained within or upon polymeric resinous (plastic) materials. As the fly height and transducer/slider size continually decrease in the progression of greater disk storage density, the accuracy and control needed to align the transducer to the correct data track upon the disk surface follows suit. The usage of thermally expansive plastics as structural elements of the suspension or head gimbal region poses dimensional stability limitations.